Stretch line on bow using touch

Question

I have drawn a line on sprite representing the string of a bow. I want to stretch it with finger touch input, using onTouch. I have added a Physics body but I don't understand how to stretch the line.

It's a bow and arrow demo:

Here is the code I use:

protected Scene onCreateScene() {
        this.mEngine.registerUpdateHandler(new FPSLogger());
        mScene = new Scene();
        mScene.setBackground(new Background(0.3f, 0.8f, 0.9f));
        float centerX = CAMERA_WIDTH/2;
        float centerY = CAMERA_HEIGHT/2;

        Sprite sprite = new Sprite(centerX,centerY,this.regionBow, this.getVertexBufferObjectManager());
        mScene.attachChild(sprite);

        PhysicsWorld physicsWorld = new PhysicsWorld(new Vector2(0, 300), false);
        Line line = new Line(99, 10, 99, 240, 4, getVertexBufferObjectManager());
        line.setColor(0f,0f,0f);

        FixtureDef lineFixtureDef = PhysicsFactory.createFixtureDef(1, 4f, 0.5f);
        Body body = PhysicsFactory.createLineBody(physicsWorld, line, lineFixtureDef);
        mScene.getLastChild().attachChild(line);

        PhysicsConnector physicsConnector = new PhysicsConnector(sprite, body, true, true);
        physicsWorld.registerPhysicsConnector(physicsConnector);

        mScene.setOnAreaTouchListener(new IOnAreaTouchListener() {
            @Override
            public boolean onAreaTouched(TouchEvent pSceneTouchEvent, ITouchArea pTouchArea, float pTouchAreaLocalX, float pTouchAreaLocalY) {
                return false;
            }
        });



        return this.mScene;
    }

Answer 1

Maybe you can not use physics. Something like this;

float[] bowLeftUpCornerPos =... // add Bow left-up corner positions.
float[] bowLeftDownCornerPos=... // add Bow left-down corner positions.
float[] bowLeftCenterPos=... // add Bow left center positions.

Line lineUp = new Line(bowLeftCenterPos[0], bowLeftCenterPos[1],
bowLeftUpCornerPos[0] , bowLeftUpCornerPos[1], 4, getVertexBufferObjectManager());

Line lineDown = new Line(bowLeftCenterPos[0], bowLeftCenterPos[1],
bowLeftDownCornerPos[0], bowLeftDownCornerPos[1], 4, getVertexBufferObjectManager());
.
.

@Override
public boolean onAreaTouched(TouchEvent pSceneTouchEvent,     ITouchArea pTouchArea, float pTouchAreaLocalX, float pTouchAreaLocalY) {

    float pX = pSceneTouchEvent.getX();
    float pY = pSceneTouchEvent.getY();

    if (pSceneTouchEvent.isActionDown() || pSceneTouchEvent.isActionMove()) {
       lineUp.setPosition(pX,pY,bowLeftUpCornerPos[0],bowLeftUpCornerPos[1]);
       lineDown.setPosition(pX,pY,bowLeftDownCornerPos[0],bowLeftUpCornerPos[1]); 
    }

    if (pSceneTouchEvent.isActionUp()) {
       lineUp.setPosition(bowLeftCenterPos[0], bowLeftCenterPos[1],bowLeftUpCornerPos[0],bowLeftUpCornerPos[1]);
       lineDown.setPosition(bowLeftCenterPos[0], bowLeftCenterPos[1],bowLeftDownCornerPos[0],bowLeftUpCornerPos[1]);
    }

return false;
}